I never understood why Data couldn't succeed at making an android. In "A Measure of a Man," there's a certain problem in building a positronic net that Data relays to Commander Maddox while in the observation lounge. My question is why Data didn't copy his own design exactly---as a working android, his design obviously allows for a functioning android---so why not use this precise blueprint for Lal?

That's exactly what he did, & apparently achieved a certain amount more success than Maddox ever did

The way Maddox seemed to believe was that the only true way to identify all the specific properties involved in Data's positronic matrix was to dissemble it & essentially study it in a non-functioning state

& since Lal faltered, perhaps there's some truth to that notion, even if it's not worthwhile to do so, & jeopardize Data's life

What boggles my mind more is that Soong would have to know he wouldn't live forever, & with the success of Data, he should have bestowed upon him every single bit of design parameters on the properly functioning Soong type android